st: Combining ROC curves in one graph

Dear Stata-users,
I have plotted three ROC curves using
roctab x1 y1, graph name(rocgraph1) nodraw
roctab x2 y2, graph name(rocgraph2) nodraw
roctab x3 y3, graph name(rocgraph3) nodraw
How can I combine these three roclines into one graph. || or (...) do not seem to work.
Moreover, I would like to do the same thing after rocfit and rocplot:
rocfit x1 y1
rocplot, confband name(rocfit1) nodraw
rocfit x2 y2
rocplot, confband name(rocfit2) nodraw
rocfit x3 y3
rocplot, confband name(rocfit3) nodraw
Thank you for your advice.
P.S. I don't want to array the separately drawn graphs into one using graph combine. I just need one graph that contains all three ROC lines.
Best regards,
Kim
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